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### msgpack extension
The msgpack extension implements encode to and decode from the [MessagePack](http://msgpack.org/index.html) data format.
You can either parse into or serialize from a variant-like data structure, [basic_json](../basic_json.md), or your own
data structures, using [json_type_traits](../json_type_traits.md).
[decode_msgpack](decode_msgpack.md)
[basic_msgpack_cursor](basic_msgpack_cursor.md)
[encode_msgpack](encode_msgpack.md)
[basic_msgpack_encoder](basic_msgpack_encoder.md)
[msgpack_options](msgpack_options.md)
#### Mappings between MessagePack and jsoncons data items
MessagePack data item |ext type | jsoncons data item|jsoncons tag
-------------------------------------------------- |-----------------|---------------|------------------
nil | | null |
true, false | | bool |
negative fixnum, int 8, int 16, int 32, int 64 | | int64 |
positive fixnum, uint 8, uint 16, uint 32, uint 64| | uint64 |
float32, float64 | | double |
fixstr, str 8, str 16, str 32 | | string |
bin 8, bin 16, bin 32 | | byte_string |
fixext1, fixext2, fixext4, fixext8, fixext16, ext8, ext16, ext32 |0-127| byte_string |
4 byte length |-1 (timestamp 32) |uint64| seconds
8 byte length |-1 (timestamp 64) |string| epoch_nanosecond
12 byte length |-1 (timestamp 96) |string| epoch_nanosecond
array | | array |
map | | object |
### Examples
#### ext format code example
```cpp
#include <jsoncons/json.hpp>
#include <jsoncons_ext/msgpack/msgpack.hpp>
#include <cassert>
using namespace jsoncons;
int main()
{
std::vector<uint8_t> input = {
0x82, // map, length 2
0xa5, // string, length 5
'H','e','l','l','o',
0xa5, // string, length 5
'W','o','r','l','d',
0xa4, // string, length 4
'D','a','t','a',
0xc7, // ext8 format code
0x06, // length 6
0x07, // type
'f','o','o','b','a','r'
};
ojson j = msgpack::decode_msgpack<ojson>(input);
std::cout << "(1)\n" << pretty_print(j) << "\n\n";
std::cout << "(2) " << j["Data"].tag() << "(" << j["Data"].ext_tag() << ")\n\n";
// Get ext value as a std::vector<uint8_t>
auto v = j["Data"].as<std::vector<uint8_t>>();
std::cout << "(3)\n";
std::cout << byte_string_view(v) << "\n\n";
std::vector<uint8_t> output;
msgpack::encode_msgpack(j,output);
assert(output == input);
}
```
Output:
```
(1)
{
"Hello": "World",
"Data": "Zm9vYmFy"
}
(2) ext(7)
(3)
66,6f,6f,62,61,72
```
#### JSON to message pack
Input JSON file `book.json`
```json
[
{
"category": "reference",
"author": "Nigel Rees",
"title": "Sayings of the Century",
"price": 8.95
},
{
"category": "fiction",
"author": "Evelyn Waugh",
"title": "Sword of Honour",
"price": 12.99
}
]
```
```cpp
#include <jsoncons/json.hpp>
#include <jsoncons_ext/msgpack/msgpack.hpp>
using namespace jsoncons;
int main()
{
std::ifstream is("input/book.json");
ojson j1;
is >> j1;
// Encode ojson to MessagePack
std::vector<uint8_t> v;
msgpack::encode_msgpack(j1, v);
// Decode MessagePack to ojson
ojson j2 = msgpack::decode_msgpack<ojson>(v);
std::cout << pretty_print(j2) << '\n';
// or to json (now alphabetically sorted)
json j3 = msgpack::decode_msgpack<json>(v);
// or to wjson (converts from utf8 to wide characters)
wjson j4 = msgpack::decode_msgpack<wjson>(v);
}
```
Output:
```json
[
{
"category": "reference",
"author": "Nigel Rees",
"title": "Sayings of the Century",
"price": 8.95
},
{
"category": "fiction",
"author": "Evelyn Waugh",
"title": "Sword of Honour",
"price": 12.99
}
]
```
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